Light directing structure



July 19, 1966 w s, MILLER 3,261,975

LIGHT DIRECTING STRUCTURE Original Filed Aug. 15, 1962 WEAJDELL. M/LLEE I N VENI OR.

United States Patent 2 Claims. (Cl. 24041.3)

This application is a division of my copending appli cation Serial No. 217,092 filed August 15, 1962 for Radiation Directing Structure.

This invention relates an improved type of radiation directing structure such as a searchlight, carbon arc radiation furnace, or other electro-magnetic radiation emitting unit. The invention will be discussed primarily as applied to searchlights although it will be apparent that certain features of the invention are equally applicable to the other above mentioned uses. A light directing structure embodying the invention disclosed here includes a source of radiation, such as a carbon arc, and a ray concentrating element for refracting light rays or other radiation in a manner producing a beam aimed in a predetermined direction, and is centered essentially about a particular axis.

Carbon arcs suitable for searchlight usage may be described as possessing two electrodes, one charged positively and the other negatively, in juxtaposition. Upon the flow of electric current a portion of the surface of the positive electrode opposite the negative electrode is heated to incandescence by the bombardment of electrons and while still in a condensed state, perhaps molten, emits light. The concentrating element employed in this species of the invention is a lens of any type suitable for searchlights. As seen from the point of light emission, the lens occupies a portion, but not all, of the 2 pi steradiams of solid angle symmetrically disposed about the above mentioned particular axis.

In designing a searchlight, it is usually impossible to provide a lens which can occupy the entirety of the above mentioned 2 pi steradiam angle, and which can effectively refract all of the emanated rays into proper alignment in the ultimate projected beam. Consequently, in conventional searchlight structures and the like the radiation within a portion of the above mentioned solid angle which contains the lens is almost invariably wasted and does not form a part of the emitted beam.

The general object of the present invention is to conserve the energy which is lost in ordinary searchlight arrangements and the like by failure to intercept the concentrating lens, and to utilize that energy in a manner acting to increase the efliciency of radiation, lengthen the active life of the radiation source, and/ or increase the brightness of the projected beam. This result is obtained by providing unique supplemental reflectors which are positioned within the above mentioned solid angle to receive the radiation emitted by the source into that solid angle and not intercepted by the lens. The function of the supplemental reflectors is to reflect such energy as would otherwise be wasted back toward the source to assist in maintaining or increasing its temperature and brightness. The supplemental reflector or reflectors preferably take the form of ellipsoids of revolution and for maximum ease of manufacture may be shaped as spheres centered about the radiation source, a sphere being a special case of an ellipsoid of revolution. The most efficient form for such an ellipsoid, although more diflicult to manufacture, is an oblate ellipsoid the focii of Whose axial section lie within, preferably near the extreme of, the diameter of the light source.

The above and other features and objects of the invention will be better understood from the following 3,261,975 Patented July 19, 1966 detailed description of the typical embodiment illustrated in the accompanying drawing in which:

The figure is an axial section of a searchlight constructed in accordance with the invention.

In this figure the searchlight at 10a utilizes a lens 26a for concentrating or directing the light rays to the left along lines such as those represented by arrows 27a. The carbon electrode of the carbon arc is represented at 17a, and co-acts with an iron electrode 18a to produce an arc, with the resulting light being considered as emanating primarily from a point 25a at the front side of the carbon electrode. Iron electrode 18a may be rigidly mounted in the illustrated position by a suitable spider 21a, while the carbon electrode may be actuable axially along axis 12, and toward and away from electrode 18a by an adjusting knob 22a. Electric current for actuating the arc may be supplied to the electrodes through leads and any conventional carbon are power source as is customary with such apparatus.

The light produced by formation of an electric are between electrodes 17a and 18a emanates primarily from a small pool or projection of high temperature carbon at 25a, a point located in the center of the forwardly facing surface of the carbon electrode. The light from the source at 25a which actually reaches and is refracted by lens 26:: falls with an angular range designated by the letter d in the figure. This angle d does not occupy the entire half space viewed from the point 25a on looking forwardly in the direction of light projection from that point, that is the half space which is forwardly of a plane which extends transversely of the axis 12 and through the light source 25a. The term half space here refers, of course, to the mathematical concept of a symmetrical 2 pi steradiam solid angle. To conserve the energy of the radiation emitted from point 25a within the rest of that half space, I provide an angular supplemental reflector 32a, which is essentially centered about the point 25a, and acts to reflect radiation emanating from source at 25a within a solid angle 2 directly back to the source. Mirror 32a may be rigidly mounted in the illustrated position in any suitable manner, as by connection to housing 11a through brackets 34a.

Mirror 32a has an inner specular reflective concave surface facing toward and centered essentially about the point 25a to attain the desired purpose of returning to the incandescent radiator light emitted therefrom within the solid angle e occupied by the supplemental mirror.

With more specific regard to the shape of the mirror 32a, the mirror should be in ellipsoid of revolution, formed by revolving about axis 12 ellipses whose focii are located at approximately the position of light source at 25a. It will be apparent that this light source may have a substantial extent transversely of axis 12, and therefore the focii of the specified ellipses may be off-set somewhat from the axis 12, preferably at diametrically opposite sides of the light source. Such ellipsoids are known as oblate spheroids. For simplicity of manufacture, satisfactory results may in most cases be obtained by forming reflector 32a as a spherically curved surface centered about the exact center of the light source at 25a which is of course located on axis 12.

In using the searchlight of the figure the operator supplies current to the electrodes to develop an arc of the appropriate length between the electrodes 17a and 18a. The light and heat energy produced at point 25a then radiates outwardly throughout the entire half space to the left of point 25a and centered on axis 12. The portion of that radiation which falls within the angular region d is refracted by lens 26a to form a beam projected outwardly to the left from the device. The energy radiating within the solid angle 2 on the other hand cannot strike or be utilized by the lens 26a but instead strike the mirror 32a and is reflected through an essentially 180 reflection by this mirror directly back to the source at 25a. To the extent this radiation is absorbed, it supplements the heating of the electrode at 25a by the are. To the extent it is either absorbed or reflected it therefore tends to increase the brightness of the beam produced by the searchlight, reduce the amount of current drawn by the light, and in general increase the operating efliciency of the searchlight as a whole.

I claim:

1. A radiation directing structure defining an axis, said structure comprising a solid electrode, material in a condensed state on one end of the said electrode and on said axis adapted to be electrically excited to emit radiation from its surface, said material defining a plane ilicrethrough perpendicular said axis, a retracting structure of positive optical power optically co-axial with said axis and having a focal point at said material, said refracting structure lying in a direction from said plane into which said material may emit radiation, a reflecting structure comprising a mirror in the form of a portion of a sphere extending outwardly from said plane in the same direction as lies said retracting structure, said spherical mirror being centered on said focal point of said refracting structure and being provided with an axial opening through which said retracting structure may be seen from said material.

2. A radiation directing structure defining an axis, said structure comprising a solid electrode, material in a condensed state on one end of said electrode and on said axis adapted to be electrically excited to emit radiation from its surface, a refractive structure comprising a lens of positive optical power, said refractive structure being optically co-axial with said axis and having a focal point at said material, said lens lying in a direction from said plane into which said material may emit radiation, reflecting structure comprising a mirror in the form of a portion of an oblate spheroid the focii of whose defining ellipses are located at said material, said portion extending outwardly from said plane in the same direction as lies said lens, said oblate spheroidal mirror being centered on said focus of said lens and being provided with an axial opening through which said lens may be seen from said material.

References Cited by the Examiner UNITED STATES PATENTS 445,379 1/1891 Peral 24041.3 2,026,478 12/1935 Lisintzki 240-41.3

NORTON ANSHER, Primary Examiner.

C. C. LOGAN, Assistant Examiner. 

1. A RADIATION DIRECTING STRUCTURE DEFINING AN AXIS, SAID STRUCTURE COMPRISING A SOLID ELECTRODE, MATERIAL IN A CONDENSED STATE ON ONE END OF THE SAID ELECTRODE AND ON SAID AXIS ADAPTED TO THE ELECTRICALLY EXCITED TO EMIT RADIATION FROM ITS SURFACE, SAID MATERIAL DIFINING A PLANE THERETHROUGH PERPENDICULAR SAID AXIS, A REFRACTING STRUCTURE OF POSITIVE OPTICAL POWER OPTICALLY CO-OXIAL WITH SAID AXIS AND HAVING A FOCAL POINT AT SAID MATERIAL, SAID REFRACTING STRUCTURE LYING IN A DIRECTION FROM SAID PLANE INTO WHICH SAID MATERIAL MAY EMIT RADIATION, A REFLECTING STRUCTURE COMPRISING A MIRROR IN THE FORM OF A PORTION OF A SPHERE EXTENDING OUTWARDLY FROM SAID PLANE IN THE SAME DIRECTION AS LIES SAID REFRACTING STRUCTURE, SAID SPHERICAL MIRROR BEING CENTERED ON SAID FOCAL POINT OF SAID REFRACTING STRUCTURE AND BEING PROVIDED WITH AN AXIAL OPENING THROUGH WHICH SAID REFRACTING STRUCTURE MAY BE SEEN FROM SAID MATERIAL. 